Why In the bell did my ex kiss me?

my ex girlfriend hates my freaking guts like really really hates my guts. Her parents forced us to break up about 5 years ago... I tried fighting for her but shit quickly went wrong. Parents made her block me everywhere, she kept coming back and crying saying she loves me then accused me of harassing her saying I wouldn't leave her alone. she ended up meeting someone 3 months later so I went no contract. the last time we talked was 3 years ago I tried being just friends with her but her current boyfriend was afraid she would leave him or I'd steal her away.

So fast forward today I am shopping at home depot paying for my things and she just so happens to be the person bagging my shit. she starts making awkward small talk and I notice the look on her face this girl was shit uncomfortable looking like she wanted to run. so am like truest me I don't like this anymore then you do if I known you were working here I wouldn't be shopping here. I just wanna pay for my shit and leave. So I start talking about doctor who our favorite tv show to break the awkwardness and she just out of no where starts crying. saying how she's sorry for the way she treated me during the break up, asked if we can meet to talk and offers to answer questions that would have given me closure years ago. I just give her this cold look and said maybe. Her eyes dropped so I give her a hug to show there is no hard feelings said maybe I'll see you around... as soon as I went to let go of the hug she kissed me straight in the lips. We kind of kissed 3 times before l realize what was going on and stopped it, she opened her mouth to say something but I just rush out of the door.

I have not heard from my ex since then and haven't gone back to home depot to find out why she kissed me. I did some digging she is still with the guy she was with who didn't want us being friends. She seems to be happy with him so why In the bell did she kiss me? Has anyone here ever had something like this happen to them